That's the dazed question on everyone's lips in official Washington today. For some, it's a happy daze; for others, it's a fog of depression. House Majority Leader Eric Cantor's stunning defeat in a Republican primary on Tuesday—by a not-even-close 11 points—took the political world by surprise. It's difficult to piece together what happened, and many of the reasons being proffered seem self-serving. The reality is surely a mix many factors, but here are a few leading theories.

1. Immigration: If there's a consensus explanation for what happened, it's that immigration reform sank Cantor. Brat accused Cantor of supporting amnesty for illegal immigrants over and over again. The majority leader is hardly a radical on the issue, but he worked to move some pieces of reform forward. In particular, he professed a desire to make some sort of accommodation for "DREAMers," undocumented children who were brought to the United States by their parents—although he also worked to keep a comprehensive reform bill from the House floor. Brat used these positions as a bludgeon in his race against Cantor; Cantor responded with fliers boasting he was "stopping the Obama-Reid plan to give illegal immigrants amnesty" and saying he didn't support "blanket amnesty." A pro-immigration group released a poll Wednesday pushing back, and argued that Cantor's district is actually fertile ground for immigration. But that's a minority view. Instant reaction to Cantor's loss is that it spells the death of immigration reform (assuming it wasn't dead already) and will scare Republicans away from further efforts for the foreseeable future.

2. Personality: Not everyone buys the immigration explanation. From Washington to Richmond and beyond Tuesday night, the air was thick with bipartisan Schadenfreude. Despite attaining the No. 2 position in the House, Cantor managed to alienate or at least annoy a great number of people on his way. Liberals found him smarmy and obnoxious; conservatives found him treacherous and untrustworthy. "[Cantor] and his staff have repeatedly antagonized conservatives," influential conservative Erick Erickson wrote Tuesday night. "One conservative recently told me that Cantor’s staff were the 'biggest bunch of a**holes on the Hill.' An establishment consultant who backed Cantor actually agreed with this assessment."

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To get a sense of how this happened, it's helpful to look back at Ryan Lizza's definitive profile a year ago. Cantor began his career as a fairly moderate Republican. When the Tea Party wave struck, he maneuvered himself into position as the movement's man in the GOP leadership, a guy who was less squishy than Speaker John Boehner and got what the conservatives were talking about. Boehner loyalists eyed him with some suspicion; clearly, Cantor had designs on the speakership, and they wondered if Boehner could trust his lieutenant. But the Tea Partiers never seemed to totally trust him either, put off by questions about the sincerity of his transition. Their doubts were affirmed by Cantor's vote to raise the debt ceiling and again in March, when Cantor helped to sneak a Medicare-reimbursement bill through the House on a voice vote. "Cantor lost his race because he was running for Speaker of the House of Representatives while his constituents wanted a congressman," Erickson wrote. "The Tea Party and conservatives capitalized on that with built-up distrust over Cantor’s other promises and made a convincing case Cantor could not be trusted on immigration either."

3. Trouble at home: Meanwhile, Cantor was undermining his support in the Old Dominion. One of the quirks of Virginia politics is the use of conventions rather than primaries for some races. As Jon Ward explains, the process of choosing delegates for conventions is called "slating," or choosing a slate of representative voters. In 2012, hardliners in the Virginia GOP changed the rules so that the 2013 gubernatorial nominee would be nominated at convention, which tends to favor energized, grassroots activists. That resulted in the nomination of the very conservative Ken Cuccinelli for governor; he lost to Democrat Terry McAuliffe in November. Cantor decided to push back this year to try and keep activists out, with an eye to changing the rules back by retaking control of the state central committee. The effect, one Republican operative wrote, was to "vigorously poke a nest of already-angry hornets." Meanwhile, some Virginians felt that Cantor was stinting on constituent services while he worked to raise his profile in Washington.

4. Crony capitalism: Brat may have assailed Cantor's position on immigration, but in a prescient April piece on the threats to the majority leader, Politico reported that Brat's big sell was straightforward populism. The Randolph-Macon College economics professor drew on one of the foundational themes of the Tea Party, complaining that Cantor was a crony capitalist:

The central theme of Brat’s campaign is that Cantor is beholden to business—specifically the U.S. Chamber of Commerce and the Business Roundtable.

“If you’re in big business, Eric’s been very good to you, and he gets a lot of donations because of that, right?” Brat said at the meeting. “Very powerful. Very good at fundraising because he favors big business. But when you’re favoring artificially big business, someone’s paying the tab for that. Someone’s paying the price for that, and guess who that is? You.”

5. Religion: Cantor's exit means there won't be a single non-Christian Republican member of Congress. Could faith have played a role in his defeat? Cantor, who is Jewish, has been in office since 2001. But his suburban Richmond constituency was recently redistricted and became more rural and more conservative. David Wasserman of the Cook Political Report—one of the smartest House analysts working—told The New York Times: “Part of this plays into his religion. You can’t ignore the elephant in the room.” In Brat, Cantor faced an opponent for whom Christianity was a defining characteristic.

6. Democratic crossover: Virginia's primaries are open, meaning that anyone of any party can vote. Is it possible that Democrats flooded the polls to hurt Cantor, whom they despise? A Daily Kos diarist exhorted fellow Democrats to vote Brat Tuesday afternoon, and Democrats claimed some credit. This is also the excuse Cantor's pollster used. John McLaughlin's polls were laughably bad: An internal poll leaked to the press last week had Cantor up 34 points. The pollster told National Journal's Shane Goldmacher that turnout swamped his candidate: "Over the weekend Democrats like [former Georgia Representative] Ben Jones and liberal media were driving their Democratic voters on the Internet into the open primary. Eric got hit from right and left. In our polls two weeks out Eric was stronger with Republicans at 70 percent of the vote, but running under 50 percent among non-Republicans." One has to wonder, though, how many Democrats would have been eager to vote for Brat, an even more conservative candidate, in a district that's heavily Republican and unlikely to elect a Democrat in the general election—even against an unknown like Dave Brat.